Method of extracting materials

ABSTRACT

A CARBONACEOUS MATERIAL E.G. COAL OR C OAL TAR, IS TREATED WITH A FLUID E.G. BENZENE OR ETHYLENE RESPECTIVELY, AT SUPERCRITICAL CONDITIONS TO EXTRACT PART OR ALL OF THE CARBONACEOUS CONTENT WHICH IS SUBSEQUENTLY RELEASED BY REDUCING THE PRESSURE.

United States Patent US. Cl. 208-8 11 Claims ABSTRACT OF THE DISCLOSURE A carbonaceous material e.g. coal or coal tar, is treated with a fluid e.g. benzene or ethylene respectively, at supercritical conditions to extract part or all of the carbonaceous content which is subsequently released by reducing the pressure.

This invention relates to the extraction of material by a fluid solvent recovery system which is operated above the critical temperature and pressure conditions for the extraction solvent.

It is known that when the temperature of a gas is above a certain temperature, known as the critical temperature, it is not possible to liquefy the gas by application of pressure alone. It is necessary to reduce the temperature below the said critical temperature in order to be able to liquefy the gas. We have found that it is possible under suitable conditions to dissolve a carbonaceous material by treating it with a fluid at a supercritical temperature and pressure.

An object of the invention is to extract part of a carbonaceous material by the use of a fluid at a supercritical temperature. A particular object of the invention is to obtain a coal which is either ash-free or the ash content of which is considerably reduced.

Accordingly the invention provides a method of extracting at least part of the carbonaceous content from a carbonaceous material wherein the material is treated with an extractant fluid at a supercritical temperature and at a pressure above atmospheric pressure so that the said part is absorbed into or dissolved by the extractant fluid, and subsequently the pressure is reduced so that the said part is separated from the extractant fluid.

The carbonaceous material may be a coal, a coal tar fraction, or a pitch.

Alternatively the carbonaceous material may be anthracene paste or a crude carbonisation by-product fraction, for example, naphthalene base-oil.

The operating temperature is preferably slightly above the critical temperature of the fluid and the pressure may have any convenient value e.g. 1000-3000 p.s.i. In certain cases, for example, when the material is coal, the extractant fluid is preferably a substance which is liquid at atmospheric temperature and pressure, for example, benzene.

Preferably also the extractant fluid is a hydrocarbon in the range C to C The extractant fluid may be any one of the following,

ethylene, propylene, methane, propane, butane, ammonia,

chlorine or carbon dioxide.

Alternatively the extractant fluid may be of any one of the following, benzene, toluene, pyridine, dimethylamine,

ethylamine or methylamine.

The following examples illustrate the invention.

EXAMPLE I Patented Jan. 26, 1971 ICC tile components from the ethylene gas. The separation means comprises separation sections in which the pressure of the gas and volatile components is stepwise reduced to atmospheric pressure. With this decrease in pressure the tar is separated into heavier and lighter fractions i.e. pitch and oils. Over 55% of volatile oils are extracted by the ethylene gas, and the solid residue-pitch has a softening point of 115 C. (ring and ball test).

EXAMPLE II The coal-tar in Example I is replaced by a pitch C. ring and ball softening point). This is treated with ethylene gas under the same conditions as described in Example I. In this way volatile oils are extracted from the pitch by the extractant ethylene gas and the softening point of the solid residue is increased.

EXAMPLE III The coal tar in Example I is replaced by anthracene paste and extraction effected as described in Example I. Relatively pure anthracene and naphthalene are recovered by this method.

EXAMPLE IV Coal is treated with benzene (critical temperature 288 C.) at a temperature of 300 C. and at a pressure of 1750 psi. Carbonaceous matter is thereby extracted into the gaseous benzene extractant leaving mineral matter undissolved. The extractant together with carbonaceous matter is fed to separation means wherein the carbonaceous matter is recovered. This results in a coal which is either ashfree, or which has a reduced ash content.

In all the above Examples I-IV the extractant fluid which is separated from the volatile components by stepwise reduction in pressure, is recompressed and recycled.

In a further application of the method of the invention, coal is carbonized in the presence of an extractant fluid maintained at supercritical conditions.

In order to obtain a high yield of extract, it is necessary to heat the coal so as to release the volatiles initially from the coal structures. At temperatures up to approximately 350 C., extraction is possible without carbonization in the normal sense. However, this does not preclude the use of higher temperatures whereby the coal would be carbonized and the carbonization products carried off by the extractant fluid. This may be effected by introducing the extractant into the carbonizer, and in the case of a fluidized bed type of carbonizer the extractant could be introduced either above or below the bed level. By controlling the extent of the volatile extraction the yield of solid material could be maintained relatively high whilst if the extraction is carried out to the ultimate limits a large proportion of the coal may be transferred to the gas phase.

We claim:

1. A method of extracting at least part of the carbonaceous content from a carbonaceous material selected from the group consisting of coal, coal tar, pitch, and anthracene paste comprising:

treating said carbonaceous material with a solvent selected from the group consisting of ethylene, propylene, methane, propane, butane, ammonia, chlorine, carbon dioxide, benzene, toluene, pyridine, dimethylamine, ethylamine, and methylamine at a temperature above said solvents critical temperature and at a pressure in the range from 1000 to 5000 psi such that said solvent is in the purely gas phase whereby said part of the carbonaceous content is removed from said material, and

reducing said pressure to a lower pressure at which said part separates from said solvent.

2. A method according to claim 1 wherein the extractant fluid is separated from the said part by stepwise reduction in pressure and is then recompressed and recycled for further extraction.

3. A method according to claim 1 wherein the carbonaceous content is extracted from the material in a plurality of stages so as to extract a part at each stage.

4. A method of extracting at least part of the carbonaceous content from coal comprising:

treating said coal with benzene at a supercritical temperature in the range of from 290 to 360 C. and at a pressure in the range of from 1000 to 5000 p.s.i. whereby said part of the carbonaceous content is removed from said coal by said supercritical benzene, and

reducing said pressure to a lower pressure at which said part separates from said benzene, said part having an ash content considerably less than the ash content of said original coal.

5. The method according to claim 4 in which said coal is treated with said benzene at a supercritical temperature of 300 C. and at a pressure of 1750 p.s.i.

6. A method of extracting at least part of the carbonaceous content from coal tar comprising:

treating said coal tar with ethylene gas at a supercritical temperature in the range of from 20 to 125 C. and at a pressure up to 5000 p.s.i. whereby said part is removed from said tar by said supercritical ethylene, and

reducing said pressure to a lower pressure at which said part separates from said ethylene.

7. The method according to claim 6 in which said coal tar is treated with ethylene gas at a supercritical temperature of 25 C. and at a pressure of 3000 p.s.i.

8. A method of extracting at least part of the carbonaceous content from anthracene paste comprising:

treating said paste with ethylene gas at a supercritical temperature in the range of from 20 C. to 125 C. and at a pressure up to 5000 p.s.i. whereby said part is removed from said paste by said supercritical ethylene, and

reducing said pressure to a lower pressure at which said part separates from said ethylene, said part comprising relatively pure anthracene and naphthalene.

9. The method according to claim 8 wherein said anthracene paste is treated with said ethylene gas at a supercritical temperature of 25 C. and at a pressure of 3000 p.s.i.

10. A method of extracting at least part of the carbonaceous content from pitch comprising:

treating said pitch with ethylene gas at a supercritical temperature in the range of from 20 C. to 125 C. and at a pressure up to 5000 p.s.i. whereby said part is removed from said pitch by said supercritical ethylene, and

reducing said pressure to a lower pressure at which said part separates from said ethylene.

11. The method according to claim 10 wherein said pitch is treated with said ethylene gas at a supercritical temperature of 25 C. and at a pressure of 3000 p.s.i.

References Cited UNITED STATES PATENTS 2,337,448 12/1943 Carr 208- 2,871,181 1/1959 Kulik 208-45 1,822,349 9/1931 Jannek 208-8 3,375,188 3/1968 Bloomer 208-8 2,049,013 7/1936 Lowry 208-8 3,240,566 3/ 1966 Bullough et a1. 208-8 3,109,803 11/ 1963 Bloomer et al 208-8 DELBERT E. GANTZ, Primary Examiner V. OKEEFE, Assistant Examiner U.S. C1. X.R. 208-45, 322, 337. 

